The present invention relates to a method for transmitting position information on a digital map and apparatus for implementing the method, and in particular to a method and apparatus for accurately transmitting position information on a digital map by using only a small amount of data.
In recent years, the number of vehicles that have on-board navigation apparatus has been increasing rapidly. The on-board navigation apparatus maintains a digital map database and is capable of displaying traffic congestion and traffic accident positions on the map based on traffic congestion information and traffic accident information provided by a traffic information center as well as performing a route search using conditions including the aforementioned information.
In Japan, digital map databases are prepared by several companies. The problem is that map data contains errors due to the different base maps and digitizing technologies. The error depends on the digital map from each publisher.
In the traffic information, for example, in case latitude/longitude data of the position is presented alone in order to report for example a traffic accident position, on-board navigation apparatus may identify a different point on the road as a traffic accident position depending on the type of the digital database maintained by the apparatus.
In order to offset such incorrect transmission of information, in the related art, node numbers are defined for nodes such as intersections in a road network and link numbers are defined for links representing roads connecting nodes. A digital map database from each publisher stores intersections and roads in correspondence to node numbers and link numbers. For traffic information, a road number is identified by a link number and a point on the road is displayed in a representation that the road is XX meters away from the start of the link.
However, node numbers and link numbers defined on a road network must be changed to new numbers in case a road is constructed or modified. When a node number or link number is changed, the digital map database from each publisher must be updated. Thus, the method for transmitting position information on a digital map requires a huge cost of maintenance.
In order to solve such problems, the inventor of the invention proposed, in the Japanese Patent Application No. 214068/1999, a system where an information providing side transmits xe2x80x9croad shape dataxe2x80x9d including a coordinate string showing the road shape in the road section of a predetermined length including the on-road position and xe2x80x9crelative position dataxe2x80x9d showing the on-road position in the road section represented by the road shape data in order to report the on-road position, and a receiving side uses the road shape data to perform map matching, identifies the road section on a digital map, and uses the relative position data to identify the on-road position in the road section. The inventor proposed, in the Japanese Patent Application No. 242166/1999, a system where xe2x80x9csupplementary informationxe2x80x9d is also transmitted including the road type, road number, number of crossing links in the road section, crossing link angles and intersection names, and a system where the transmission data amount of xe2x80x9croad shape dataxe2x80x9d is reduced without causing erroneous matching at the receiving side.
In this case, map matching at the receiving side is made for example as follows:
As shown in FIG. 21, when the longitude/latitude data of the point P0 (x0, y0), P1(x1, y1), . . . , pk(xk, yk) is transmitted as (x0, y0) (x1, y1), . . . , (xk, yk), the receiving side uses the map data read from its digital map database to select roads included in the error range about the point P0 (x0, y0) as candidates, and narrows down the candidates by using the transmitted xe2x80x9csupplementary information.xe2x80x9d When a single candidate is finally selected, a position closest to the point P0 (x0, y0) and the point Pk (xk, yk) on the road is obtained, and the section is assumed as a road section represented by the xe2x80x9croad shape data.xe2x80x9d
When the final candidate is not selected but the roads Q, R are selected as candidates, the points Q0, R0 on the candidate roads closest to the point P0 (x0, y0) are obtained to calculate distance between P0 and Q0 and the distance between P0 and R0. This operation is repeated for each point P1(x1, y1), . . . , Pk(xk, yk) and a road section where the sum of the root mean square of the distances from each point P0, P1, . . . , pk is smallest is obtained. This section is assumed as a road section represented by xe2x80x9croad shape dataxe2x80x9d to identify the road section.
The traffic congestion section A-B is identified based on xe2x80x9crelative dataxe2x80x9d transmitted from the start point of the road section obtained from xe2x80x9croad shape data.xe2x80x9d
In the system where road shape data is transmitted, however, how to reduce the transmission data amount without degrading the information accuracy is a major problem. The inventor, in order to reduce the data amount, proposed a system whereby the shape data of the linear road sections is reduced and a system where the curve shape of a road is represented by Fourier coefficients, approximated by arcs, or represented by spline function to compress the data amount. In case, as shown in FIG. 23, the road density is low but the road shape is complicated and an interval between nodes is longer, as on the roads in the mountains, using such a system still requires a large amount of data to represent the road shape.
The invention solves such related art problems and aims at providing a position information transmission method for accurately transmitting a position and a shape on a digital map using a small amount of data and apparatus for implementing the method.
According to the invention, a position information transmission method wherein the transmitting side transmits road shape information to specify the target road section on a digital map and event information to specify an event position by using a relative position in the target road section and the receiving side performs map matching based on the road shape information to identify the target road section and identifies the event position in the target road section based on the event information is characterized in that the transmitting side intermittently selects nodes included in the target road section to include the coordinate data of the nodes in the road shape information for transmission, and that the receiving side performs map matching to determine the positions of the nodes included in the road shape information and obtains the road connecting the nodes by way of a route search to identify the target road section.
The transmitting side evaluates the potential for erroneous matching of the nodes in the target road section at the receiving side, and determines the length of the target road section or the number of nodes to be included in the road shape information.
The present invention also provide a position information transmission apparatus for transmitting road shape information to specify the target road section on a digital map and event information to specify an event position by using a relative position in the target road section. The transmission apparatus is characterized in that the apparatus includes position information converting means for selecting a target road section having the event position and transmit node extracting means for intermittently selecting nodes to be included in the road shape information out of the nodes arranged on the target road section.
The present invention further provide a position information receiving apparatus for receiving road shape information to specify the target road section on a digital map and event information to specify an event position by using a relative position in the target road section is characterized in that the apparatus comprises map matching means for performing map matching to determine the positions of the nodes included in the road shape information and route search means for obtaining the road connecting the nodes determined to reproduce the target road section.
This makes it possible to transmit event positions on a digital map efficiently and accurately with a small data amount thus enhancing the data transmission efficiency.